Background: The Veterans Metrics Initiative (TVMI) Study is the first study to provide a comprehensive examination of military veterans' experiences as they transition from military service. While suicidality was not a primary focus, veterans were asked about experience of suicidal thoughts, as well as life circumstances that may contribute to suicidal thoughts, at each of six timepoints of this three-year study. The current study proposes to leverage these data to examine several important questions pertaining to veterans' suicidal thoughts during transition. Results can inform the identification of veterans at greatest risk for suicidal thoughts during transition and inform interventions aimed at interrupting trajectories that increase risk for suicide. Significance/Impact: This study will provide critical insight into how veterans' experiences of suicidal thoughts change throughout the military to civilian transition, what factors are associated with increases and decreases in suicidal thoughts during transition, and which veterans are most vulnerable to suicidal thoughts following transition. This study is responsive to HSR&D's request for research on veterans' suicidality following transition from military service, as well as key priorities outlined in both VA's National Roadmap to Empower Veterans and End Suicide and the National Strategy for Preventing Veteran Suicide. Innovativeness: The proposed study is innovative in several ways. First, it represents the first in-depth investigation of veterans' suicidal thoughts during their transition from military service. Second, its longitudinal design provides a unique opportunity to isolate factors that lead to changes in suicidal thoughts over time. Third, it offers a much more comprehensive assessment of risk and resilience factors for suicidal thoughts than prior research, drawing from measures of a wide variety of vocational, financial, health, and social experiences that may contribute to suicidality. Fourth, its population-based nature allows for attention to the experiences of veterans who are not adequately represented in prior research, including both non-VA users and veterans from all service branches. Fifth, the sample is large enough to support the type of sophisticated analyses needed to adequately characterize the complexity underlying veterans' suicidal thoughts, as well as separate analyses of smaller subgroups (e.g., female veterans). Specific Aims: Aim 1 is to identify factors present at separation that are associated with veterans' suicidal thoughts within the first year after separation. Aim 2 is to identify post- separation vocational, financial, health, and social experiences that are associated with increase or decreases in suicidal thoughts during transition, either independently or in combination with separation factors. Aim 3 is to identify differences in risk for suicidal thoughts during transition for three high-risk veteran subgroups - female veterans, non-users of VA care, and veterans who live in rural locations, as well as to examine unique risk and resilience factors for suicidal thoughts among each of these groups. Methodology: Over 9500 Veterans participated in a first assessment within approximately three months following separation. Five follow-up assessments were implemented at six-month intervals thereafter, with retention rates ranging from 63% to 77% across timepoints. Analyses will include machine learning, growth curve modeling, and linear and logistic regression. Next Steps/Implementation: Study findings and implementation recommendations will be shared with VA policymakers and clinical leaders following completion of the study.